1. Field of the Invention
This invention relates to a roll cooling method for cooling cold steel strips, and more particularly to a method of cooling steel stripe with rolls in a heat treatment line, particularly continuous annealing process line or continuous plating line.
2. Description of the Prior Art
It has been generally known to continuously cool a cold steel strip in contact with and running about a hollow roll with the aid of heat transfer between the steel strips and a cooling medium flowing through an inner cavity of the roll. However, the steel strip cooled by such a roll cooling method often does not keep its flatness after cooled and tends to cause defects such as wave-like deformations, wrinkles or folds which inadmissibly reduce its value in article of commerce.
There are two factors making defective the shape or appearance of the steel strip. One relates to an accuracy of an apparatus, such as deviated shapes of cooling roll surfaces, dirty surfaces of the cooling rolls, incorrect setting of the cooling rolls and the like. The other relates to an operating condition such as unsuitable selections of cooling roll diameters, lengthwise tensile forces acting upon steel strips, cooling extent for steel strips, winding angles of the steel strips which are central angles at centers of the rolls subtended by parts of the steel strips wound about the rolls, and the like.